Field
Embodiments of the present disclosure generally relate to increasing UV penetration in flowable layers. More specifically, embodiments described herein generally relate to methods for pretreating a flowable layer for increased curing efficiency.
Description of the Related Art
Semiconductor device geometries have dramatically decreased in size since their introduction several decades ago. Modern semiconductor fabrication equipment is routinely used to produce devices having geometries as small as 28 nm and less, and new equipment designs are continually being developed and implemented to produce devices with even smaller geometries. As device geometries decrease, the impact of interconnect capacitance on device performance increases. To reduce interconnect capacitance, inter-layer materials that have traditionally been formed of silicon oxide are being formed using lower dielectric constant materials (low k materials). Some low k materials that have been used include fluorinated silicon oxide, carbonated silicon oxide, and various polymers and aerogels. Use of these low k materials often presents serious reliability, manufacturability, and/or integration challenges.
Over the years, many techniques have been developed to avoid having dielectric material clog the top of a gap, or to “heal” the void or seam that has been formed. One approach has been to start with highly flowable precursor materials that may be applied in a liquid phase to a spinning substrate surface (e.g., spin on glass deposition techniques). These flowable precursors can flow into and fill very small substrate gaps without forming voids or weak seams. However, once these highly flowable materials are deposited, they have to be hardened into a solid dielectric material.
In many instances, the hardening process for flowable materials includes a non-thermal curing under UV lights, to further crosslink the materials into a film, before furnace conversion and densification. With UV exposure, the film density and Si—Si bonds increase. As the surface is the first region of the film to come in contact with the UV radiation, the optical property of the film changes at the surface first. The reflective index and extinction coefficient increase for the surface layer, and this blocks or reduces UV intensity in the bulk film.
Accordingly, devices and methods for better controlling the UV cure process are desirable.